A woman wears a face mask on a grey day in Beijing. Authorities in Shanxi have set targets to reduce concentrations of harmful PM2.5 particles and sulphur dioxide levels by 40 per cent over the winter months. Photo: AP

A woman wears a face mask on a grey day in Beijing. Authorities in Shanxi have set targets to reduce concentrations of harmful PM2.5 particles and sulphur dioxide levels by 40 per cent over the winter months. Photo: AP